It is well known in the art that in establishing communications between DCE's or modems, a training sequence may be sent between the data circuit terminating equipment (DCE) or modem sending the information to the DCE or modem receiving the information prior to the transmission of actual data. The training sequence is typically used for synchronization purposes and also for permitting the receiving modem to detect and compensate for the amplitude and phase delay characteristics of the channel over which the data is to be sent. The compensation of the intersymbol interference is achieved by the use of equalizers or adaptive equalizers located in the receiving modem which analyzes the received training sequence and adapts its coefficients accordingly. However it has appeared that in some situation it is impossible for a modem which is connected to a telecommunication network to transmit or receive any training sequence.
FIGS. 1 and 2 shows two typical examples in which no training sequence is allowed. In FIG. 1, a base-band modem 101 is connected to a digital network 103 via an input node 102. The network does not authorize the base-band modem 101 to transmit and to receive any training sequence through the digital network. The latter modem has to adjust its equalizer directly without the use of a training pattern. FIG. 2 illustrates a similar case of a multipoint network 203 in which a control station 201 communicates with some tributary stations 202. Since the connection of an extra tributary station 202 should not interrupt the communication of the already existing stations, the equalizer system included in this supplementary station has to adjust its coefficient without the use of any training sequence.